We have completely characterized which unitary Cayley graphs are Ramanujan. Weremark that every case of Theorem 1 gives rise to infinite families of Ramanujan graphsin this form. As shown by Murty in [Murty (2005)], it is impossible to construct an infinitefamily of k-regular abelian Cayley graphs which are all Ramanujan for any particular k.However, finding examples of Ramanujan graphs in the way that we have presented hereis still of some interest. It is also interesting to remark on some other work that has beendone on unitary Cayley graphs. Various properties of the graph Xn were determined in[Klotz, W. and Sander, T. (2007)], including the chromatic number, the clique number,the independence number, the diameter, and the vertex connectivity, in addition to somework on the eigenvalues. The energy of Xn was determined and studied independentlyin [Ili´c (2009)] and [Ramaswamy, H.N. and Veena, C.R. (2009)]. It is also interesting tonote that [Ramaswamy, H.N. and Veena, C.R. (2009)]...